Experiments using intracellular and extracellular recording techniques have been conducted on cells cultured from the mammalian central nervous system (CNS) and a clonal pituitary line. The work has focussed primarily on characterizing the types of excitable membrane properties resident in these cells and secondarily on studying the effects of transmitters, hormones and drugs on these properties. The principal conclusion are 1) that multiple types of electrically and chemically excitable membrane properties are present in both cultured central neurons and endocrine cels and 2) that in the case of primary CNS neurons these properties become expressed before birth. Two properties--chemically regulated Cl-ion conductances and electrically activated transient-type K+ conductances--have received the most study primarily because these properties are expressed in virtually every nerve cell cultured from spinal and hippocampal regions. The K+ conductances are also found in clonal pituitary cells. Recent insights in to these conductance mechanisms include the following: The kinetics of pharmacologically evoked Cl-ion channel behavior are markedly voltage-sensitive so that at depolarized potentials more channels open for a longer duration. Synaptically activated Cl-ion dependent conducatances mediated by gamma-aminobutyric acid (GABA) show a similar sensitivity to voltage. Thus, GABA-mediated synpatic potentials are effectively more inhibitory at depolarized potentials. In clonal pituitary cells transient-type K+ conductances, which function to regulate the rate of action potential discharge, are modulated by releasing factor peptides. This modulation accounts for the actions of these peptide hormones in altering the excitability of these cells. Convulsant drugs and transmitters also appear capable of modulating the excitability of central neurons through actions on transient type K+ conductances. These results receptors and ion conductance mechanisms in specific types of excitable nerve and endocrine cells.